1. Field of the Invention
The present invention relates to an oil passage structure in a rotary shaft that is applied to a transmission of an internal combustion engine-transmission integrated type power unit for a four-wheel buggy car (saddle ride type vehicle for operating on wasteland).
2. Description of Background Art
There has hitherto been practiced a technology in which center holes extending along the center line of a rotary shaft are provided that extend from both ends of the rotary shaft. Oil supply holes are provided for connecting the center holes with portions requiring oil supply. Oil that is different in pressure, namely, a high-pressure working oil for an oil hydraulic clutch and a low-pressure lubricating oil are supplied, respectively, from both ends of the rotary shaft. Thus, two systems of oil passages are formed. Since it is necessary to supply the oil at different pressures into the center holes, the depths of the center holes bored from both ends of the shaft have hitherto been so set that the center holes are not in communication with each other in the shaft in the boring step. Therefore, the center holes have been partitioned from each other by the material of the shaft itself. Namely, the depth bottom portions of the center holes have each been machined into a dead end shape.
Oil supply holes extending in the radial direction of the rotary shaft for connecting the center holes of the shaft with portions requiring oil supply are bored in the rotary shaft from outside of the shaft. At this time, so-called burrs are generated at an end portion of each oil supply hole on the side fronting on the center hole. In the case of the center hole having the above-mentioned dead end shape, it is difficult to perform deburring, and much time has been required for the deburring step.